1. Field of the Invention
The present invention relates to a curve approach control apparatus which controls a car to make it travel a curved road at an appropriate speed.
2. Description of the Related Art
Many curve approach control apparatus have been proposed which use road map data in a navigation device to detect an overspeed state of a car with respect to a curve in front and activate an alarm or deceleration control. For example, Japanese Patent Unexamined Publication No. Hei. 4-236699(JP-A-4-236699) discloses a technology which determines an appropriate approach speed at which to enter the curve based on a radius of curvature of a curve in an optimum travel path (guided path) set in the navigation device and on detected road surface conditions and, when an actual car speed is higher than the calculated value of the appropriate approach speed, issues a warning to alert the driver to the need for reducing the car speed, or automatically activates a car speed reduction means in combination with the warning.
A method of determining a curve""s radius of curvature by using road map data in the navigation device is disclosed, for example, in Japanese Patent Unexamined Publication No. Hei. 11-2528 (JP-A-11-2528) filed by the applicant of this invention which describes a technology for determining the curve""s radius of curvature from nodes on the road map data of the navigation device.
As shown in FIG. 10, an exit road from an expressway or wide highway (hereinafter referred to as a main road) often runs almost parallel to the main road over a certain distance after branching from the main road. Suppose a guided path set in the navigation device is the exit road and that the car travels straight through the branch point between the main road and the exit road. In that case, the navigation device may falsely assume for a while that the car is running on the exit road and send node data on the exit road to a curve approach control apparatus. If the exit road has a curve immediately in front, the curve approach control apparatus performs an alarm control and a deceleration control for that curve, giving rise to a possibility of confusing the driver who is actually traveling on the main road.
When the guided path is not set, the navigation device estimates a path the car will travel according to a road kind, a road width and the like and sends the node data on the estimated path to the curve approach control apparatus. In that case, too, the similar possibility to that described above exists. That is, suppose the exit road as opposed to the main road is erroneously or inevitably set as the estimated path. When the navigation device continues to send the node data of the estimated path (exit road) despite the fact that the car is running straight on the main road, the curve approach control apparatus executes the alarm and deceleration controls for the curve that lies immediately down the exit road, with the result that the driver who is actually traveling the main road may be confused.
The present invention has been accomplished under these circumstances and provides a curve approach control apparatus which can prevent erroneous alarm and deceleration controls due to false recognition by the navigation device of the car(vehicle) travel path at the branch point between the main road and the exit road to thereby reduce a sense of incongruity the driver feels.
To solve the problem described above, a curve approach control apparatus according to a first aspect of the present invention comprises: a front road attribute calculation/storage means to set a variety of road attribute information on a road in front based on at least node information supplied from a navigation device; a decision output means to determine a curve of the road where a car is traveling based on at least the road attribute information and make a decision on an execution of an alarm control or a deceleration control; and a control execution decision means to decide whether or not to permit the execution of the alarm control or the deceleration control depending on a running state of the car traveling; and wherein the front road attribute calculation/storage means sets as road attribute information at least identification information representing whether there is an exit road from a main road on the road in front that the car is traveling; wherein the control execution decision means checks a running state of the car as the car passes through a branch node between the main road and the exit road to see whether or not it is highly likely that the navigation device has erroneously recognized a car travel path following the branch node, and when the control execution decision means decides that it is highly likely that the navigation device has erroneously recognized the car travel path following the branch node, the control execution decision means instructs a temporary inhibition of execution of the alarm control and the deceleration control.
In a second aspect according to the curve approach control apparatus in the first aspect of the present invention, when a car (vehicle) speed as the car passes through the branch node is higher than a predetermined value, the control execution decision means checks whether or not it is highly likely that the navigation device has erroneously recognized the car travel path following the branch node.
In a third aspect according to the curve approach control apparatus in the first aspect of the present invention, when the navigation device has recognized the exit road as the car travel path after the car has passed the branch node, the control execution decision means checks whether or not it is highly likely that the navigation device has erroneously recognized the car travel path following the branch node.
In a fourth aspect according to the curve approach control apparatus in the first aspect of the present invention, when the control execution decision means decides that car is traveling straight on the main road, based on a comparison between one of yaw rate, lateral acceleration and steering wheel angle that are generated in the car as it passes through the branch node and a preset value, the control execution decision means decides that it is highly likely that the navigation device has erroneously recognized the car travel path following the branch node.
In a fifth aspect according to the curve approach control apparatus in the fourth aspect of the present invention, the preset value is set variable according to the car speed.
In a sixth aspect according to the curve approach control apparatus in the first to fifth aspect of the present invention, when at least a predetermined time is elapsed after the control execution decision means has decided that it is highly likely that the navigation device has erroneously recognized the car travel path following the branch node, the control execution decision means resets the inhibition of execution of the alarm control and the deceleration control.
In a seventh aspect according to the curve approach control apparatus in the first to fifth aspect of the present invention, after the control execution decision means has decided that it is highly likely that the navigation device has erroneously recognized the car travel path following the branch node, when at least a predetermined distance is traveled by the car, the control execution decision means resets the inhibition of execution of the alarm control and the deceleration control.
In a eighth aspect according to the curve approach control apparatus in the first to fifth aspect of the present invention, after the control execution decision means has decided that it is highly likely that the navigation device has erroneously recognized the car travel path following the branch node, when at least the yaw rate detected as the car negotiates a curve is within a predetermined range which is estimated from the same curve that was recognized by the navigation device, the control execution decision means resets the inhibition of execution of the alarm control and the deceleration control.